The Schottky diode is an important power device and is widely applied for power supply switch, motor control, telecom switch, industrial automation, electrical automation, etc., and several high speed power switches. The very important position of Schottky diode is due to its good performance. For instance, the leakage current of the Schottky diode at reverse bias is acceptable even though it is larger than that of typical PN type diodes; the forward voltage drop is low; the reverse recovery time (tRR) is very short; and the resistance reaches about 250 voltages at reverse bias. However, the leakage current of Shottky diode is higher than that of PN type diodes, and the leakage current is unstable and increasing following the increasing reverse bias because the image charge potential barrier is lower. Another drawback is that the reliability of the metal-semiconductor junction is decreasing when temperature is increasing, thereby to lower the capability of Schottky diode bearing forward and reverse impulse.
There are many methods for manufacturing the dual trench rectifiers in prior art. One of them is a Taiwan patent application with serial number 101140637 proposed by the inventor of this application.
Referring to FIG. 1, the structure of a well known trench rectifier includes an active area 15A and an end area 15T. Several trenches are formed in the active area 15A of an n− epitaxy layer 105 on a heavy doped n+ semiconductor substrate 100. A trench oxide layer 10G is formed on the bottom and sidewalls of each trench. A polysilicon layer is then filled fully in the trenches. The mesas between two trenches are formed with p+ heavy doped areas 20, like two small ears hanging on the two upper sidewalls of the mesa adjacent to the trenches. A metal silicide 60 is formed on the polysilicon layer 40 and the mesas. A top metal layer 80 is formed for serving as an anode which connects the active area 15A and extends to cover a portion of the end area 15T. The end area 15T includes a big trench. An oxide layer 10, a sidewall polysilicon 40S and a trench gate oxide 10G are formed on the big trench. Another metal layer is formed on the lower surface of the heavy doped n+ semiconductor substrate 100 for serving as a cathode.